Two Gossen Luna Pros do not work correctly with the battery adaptor
Well, I thought that an older Gossen Luna Pro could be brought back to life using the offered battery adaptor that allows one to inser the adaptor into the meter, and use two modern batteries. Evidently I was wrong.
Much to my surprise, after inserting the adaptor with fresh batteriesand "zeroing" the meters, they both read exactly the same high and low values....but the values are incorrect. My Sekonic meter reads values that are considerably lower, and negatives exposed using the Sekonic are perfect.
For example, the Sekonic 508 will read EV values of 10 and 13. Both Luna Pros will read values of 13 and 16. Exposing for the shadows at an EV of 13 would be completely wrong.
Has anyone had similar problems of "high" readings with Gossen Luna Pro meters that have been equipped with the battery adaptor? Is the voltage incorrect? I had read that many who purchased the battery adaptor were pleased, and the meter was working correctly. I guess both meters could be broken...but at the same time, and reading the exact same EV values? The only common thread is the adaptor.
Thanks for the help.
For clarity, which version of the meter are you referring to? I ask because the names of the different models vary depending on where the meter is distributed from.
For one of my meters at least (I have two, and they are of different vintages) they are badged "Lunasix 3 and they have both a "Transfer Scale" and an "EV Scale". If you are reading from the "Transfer Scale" it will yield numbers that are 3 more than the corresponding numbers on the EV scale.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
Some other things to think of: the zeroing, is it done correctly? And what metering mode do you use the 508 in? Is the testing done in a controlled environment?
“Do your work, then step back. The only path to serenity.” - Lao Tzu
Keep in mind also that the Luna Pro uses a CdS metering cell, which is more sensitive to red and yellow light than the Silicon Blue Cell in your newer Sekonic. The Luna Pro will read higher in Incandescent or Tungsten light than a modern meter. Check them in daylight, if you haven't done so.
The zero value should not change when using the transfer from 2x PX625 1,35V (Mercury) to the V206A adapter 2x SR44 1,55V (Silveroxide) batteries.
The build in Schottky diode brings it back to a stable 2,7V operating voltage. Comparing the EV F/t iso values over a wide range they are within 1/3F stop of my Leica M7 metering system which is also about the same for my M645 pro AE prisma metering and even on the C.V. Bessa III 667, non TTL exposure meter. Values from 4s - 1/1000s (1/4000s (EOS) ) I can check. The very long exposure possibility from a Gossen Lunasix-3 / (3S) -4EV +20EV is over every camera metering system I have. Concerning the reciproke correction of most films it is not a big deal because +/- 20% in this area you do not see much difference.
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Thanks very much for all of the input and interesting suggestions. Let me answer the questions posed:
Both meters are Luna-Pro meters. One on them had CdS written on the lower part of the face, and the other has no further information concerning the cell.
All readings were done in daylight, several different days, directly outside my front door in Florida. I moved from sunlight to shadows and took multiple readings with all meters.
The "white dome" was in the correct position each time.
Only incident readings were taken. I tend to use incident metering, and am very familiar with the foibles of using various metesr for incident readings.
Matt-I don't see any "transfer" scale on my meters. Perhaps I am missing something quite obvious? One simply reads the EV values, and moves the dial.
I am judging the meters purely on where the red pointer moves when the measurement are taken.
I suggest Elliot you get them checked by a professional if you need a definitive answer to your questions, everybody has an opinion, but that's all they are.
This is just an opinion, but...
I use a LunaPro with adapter and the transition from merc batts to adapter was seamless. I suspect you may need to brush up on the instruction manual. I do not intend to be offensive in any way but if, on the Luna Pro, you are not taking the number indicated by the needle (Light Value) and transfering it to the calculator you are omitting the important impact of film speed on your exposure information.
I have a couple of these meters also and use the battery adapters. First, the scale read by the pointer is not in EV; you must read the pointer scale, then rotate the dial to the pointer indicated number on the yellow scale (yellow triangle) and then read the EV below that with the black triangle.
A quick check of accuracy: set ISO to 100, mode to incident reading (slide dome over center), aim at sun on bright sunny day. Reading should be 20 (plus/minus a smidge) on the pointer scale, set 20 on the yellow scale and EV should read 15. If this is so, all is well and the meter is accurate.
BTW, Gossen meters indicate about 2/3 stop higher than most Japanese calibrated meters. German meters use a different calibration protocol than Japan; German meters use 5600K vs. Japan's 3400K color temperature light sources (might be off a tad on the temps as I am recalling these numbers from memory).
The usual problem is that the protector/lens on the sensor gets cloudy from grunge/oils and the meter will read lower than normal. The meter has to be taken apart and the lens and protective cover need to be cleaned.
The Luna Pro is a great meter. The only drawback is that the meter has a bit of a 'memory;' if you have read a bright area and immediately read a much darker area, the meter needs several seconds to settle into the correct reading. This is inherent with all CdS sensors.
Last edited by Fred Aspen; 12-17-2012 at 10:16 AM. Click to view previous post history.
... and there is also the mysterious K-factor differences.
Originally Posted by Fred Aspen